It is almost a given that a great collection of anonymous, or "found," photography will haunt us in a way that photos with a full-fledged provenance often fail to do. Ripped from factual or historical context, anonymous photos epitomize the mystery of real moments, suggesting far more than they can every fully explain, leaving us with a poignant sense of reality's ephemeral nature. And this collection, by Robert Flynn Johnson--curator of the Achenbach Foundation for the Graphic Arts at the Fine Arts Museum of San Francisco--is certainly a great one, not only beautifully presented but superbly organized as well, giving thematic order to images that might otherwise swirl randomly through photographic history.

As a collector and scholar, of course, Johnson's eye is keenly attuned to the qualities that make for a fine photograph--tonal, compositional, formal, and temperamental. Many of the more than 200 images here are as remarkable as any number of classic photographs. Again and again they prove that photography remains the most democratic art form, endowing even the humblest snapshooter with the potential to capture a moment--even accidentally--that will live forever and may move us with the power of a great artwork.

Thus, Johnson's sectional approach, beginning with "Land, Sea and Sky," collects some wonderful ephemera, from the serenely picturesque--a rowboat glimpsed from afar, across a lake at sunset, beautifully and subtly occupying the center of the frame--to startling images of the moon behind clouds, or geese in their chevron flight against the moon; of lightning electrifying the night; of lava sparking from a volcano's crater; and, most powerfully, a panoramic image of a 19th-century crowd on a hill, witnessing the smoke and flame of a city on fire (Is this Chicago? San Francisco?). The sheer scale of this print is overwhelming; it is a masterpiece of documentary photography.

More intimate, of course, is everything else in this book. The section on "Beginnings" captures childhood in a plethora of ways, all compelling. A baby cradled against a mirror, twinned in the reflecting glass, with the image of the photographer and, presumably, the mother visible in the mirror, becomes something almost worthy of Velazquez's "Las Meninas," that painterly Bible of multiple visual referencing. Less ambitious but no less expressive are strange period images of children costumed as bride and groom, or smoking cigarettes, or of two white girls cradling blackfaced baby dolls. And the shot of Nazi storm troopers holding the hands of their two young children, identically dressed in miniature storm trooper outfits, is a dark wonder.

Just as fascinating: "Maturity," shots of men and women that reflect a range of adult choices and tensions. A formally dressed woman in a platinum wig stares at us, arms folded across the back of a chair, an odd floral wallpaper behind her--paging Cindy Sherman! And who are these women clustered so collegially together, wearing city clothes from the 1930s, their faces half-hidden by surgical masks? And what of this photo of a woman replacing the inner tube of a bicycle tire, a neatly crafted study in physical angularity and circular geometry?

In "Eros," Johnson brings us anonymous erotic photography, from the comically titillating--two women baring their buttocks for us, and holding their garter belts high over their heads--to formal nude portraits and fetishistic studies of female genitalia. These images tend to reek of amateurism, but the sexually charged nature of the work assures some interest. And one shot, of a nude man and woman tangled in bed, while the shadows cast above the bed by Venetian blinds provide a noir-ish atmosphere, is a formal and tonal delight, despite the posed melodrama of the whole thing.

Johnson closes out his overview with "Endings and Infamy," which collects a number of morbid images, from the formal baby-in-coffin portraits that were all the rage in the Victorian era to documentary photos of executions. One shot of a decapitation, presumably in a public square in Japan, is stunning. The head has just hit the ground, plopping chin-first with all the indelicacy of gravitational fact, while blood spurts ferociously from the headless torso and the Samurai executioner follows through with ritual dignity, his sword bloodstained. Whoever took this photo had a feel for the decisive moment to match the most darkly voyeuristic impulse--just as whoever took the wonderful, life-affirming photo of 19th-century pedestrians rushing across a Parisian street in the rain, their umbrellas tilting forward, their feet blurred in motion, was channeling the best of Lartigue or Cartier-Bresson. Enigmatic they may be, but in the end these images are all about the visual certainty and personal stamp that only the camera can bring to history. "This was here," these photos seem to say, "and so was I."

Matt Damsker is an author and critic, who has written about photography and the arts for the Los Angeles Times, Hartford Courant, Philadelphia Bulletin, Rolling Stone magazine and other publications. His book, "Rock Voices", was published in 1981 by St. Martin's Press. His essay in the book, "Marcus Doyle: Night Vision" was published this past November.